1. Field of the Invention
The present invention relates to an ink jet printing apparatus and an ink jet printing method. More particularly, the invention relates to an ink jet printing apparatus that discharges to a printing material ink and a liquid that contains a processing liquid to insolubilize or coagulate ink for printing, and also, relates to an ink jet printing method.
2. Related Background Art
The ink jet printing method has advantages such as low noises, lower running costs, and ease with which it can be fabricated more compactly, and for color use as well. This method is widely adopted for a printer, a copying apparatus, a facsimile equipment, and many others.
For the conventional ink jet printing method, there has been often used a paper sheet specially formed with an ink absorbing layer having a good water-resistance capability for obtaining a high color image without ink spreads, while maintaining a good water-resistance capability of ink on the material used for printing. However, with improvement in the quality of ink, the adoptability of use for the ink jet printing apparatus is being enhanced even to its use on an ordinary paper sheet in recent years. The ordinary sheets are used in a large quantity for a printer, a copying apparatus, or the like. Nevertheless, the quality of images printed on the ordinary sheet still remains at the level of a stage that needs more improvements. In this respect, several technical proposals have been made to attempt the enhancement of the water-resistance capability and the quality of print with respect to the use of an ordinary sheet.
As one of such proposals, there is known a method to enhance the water-resistance capability of images by improving the quality of ink, such as making the colorant contained in ink water-resistant. However, the ink used for such method is fundamentally hard to be dissolved again by water after drying. Therefore, the discharge ports and others of the printing head tend to be clogged. It may be possible to prevent this from taking place, but the structure of the apparatus should become more complicated inevitably.
Also, a method is disclosed in the specification of Japanese Patent Laid-Open Application No. 56-84992 to coat a material to fix dyes in advance on a printing material. However, this method makes it necessary to use a specific printing material that enables such fixing material to be coated on such material. Also, in order to coat the material to fix dyes in advance, the apparatus should be made larger, leading to the inevitable cost increase. Furthermore, it is comparatively difficult to coat such material to fix dyes stably on a printing material in a given film thickness.
Furthermore, for the enhancement of the quality of printed images, it is necessary to satisfy the aspects given below.
1. Characters and images should be printed sharply so that no feathering occurs to blur the edges of dot configurations irregularly when formed by discharged ink; and
2. Images should be printed clearly without any bleeding caused by the mixture of different colors of ink at boundaries between them.
However, in order to prevent the occurrence of feathering referred to in the above paragraph 1, there is a need for ink not to be permeated into the printing material. Here, the water-based ink that is usually used for the performance of an ink jet method is liable to create bleeding. On the contrary, if it is made to allow ink to permeate into a printing material, feathering tends to take place, although the occurrence of bleeding referred to in the above paragraph 2 can be reduced.
With a view to solving the problems described above, a technique is proposed in the specifications of Japanese Patent Laid-Open Application No. 64-63185 and Japanese Patent Laid-Open Application No. 61-249755, among some others, in which an arrangement is made to cause a colorless liquid that insolubilizes dyes to adhere to a printing material together with ink by use of an ink jet head.
In accordance with such technique, it is possible to obtain a high water-resistance capability, because color ink is insolubilized and fixed on a printing material. Also, it becomes possible to suppress the occurrences of feathering and bleeding at a time if such processing liquid is provided under a given condition in advance.
However, there is still a problem that it takes a time to fix ink, because this method requires a larger amount of liquid to be applied to a printing material in total.
To avoid this problem, it is effective to arrange the fixing speed faster by making either one or both of ink and processing liquid easily permeative into a printing material.
If a permeative ink is provided before processing liquid, feathering takes place because ink permeates into the irregular meshes of a paper sheet. However, if a permeative processing liquid is provided before the application of ink, colorant in ink is insolubilized or coagulated by such processing liquid make ink not to be easily permeated, thus reducing the occurrence of feathering. The resultant image quality is improved significantly.
In the meantime, if non-permeative ink is applied before the provision of processing liquid, it becomes possible to form images of excellent quality with almost no feathering.
Compared to the so-called preceding application, that is, processing liquid is provided before ink, a smaller amount of processing liquid is needed for the so-called post-application, that is, the permeative ink is applied before the provision of processing liquid when used for obtaining the water-resistance capability of a same degree. Therefore, it has an advantage that the running costs are made lower. This is due to the fact that in order to effectuate the provision of water-resistance capability, it is good enough if only the colorant existing near the surface layer of a paper sheet should be insolubilized or coagulated, and it is not considered necessary to permeate the processing liquid further into the deeper layer of the paper sheet.
Nevertheless, there is still a problem that bleeding takes place if non-permeative ink of different colors are in contact with each other on a paper sheet.